To meet the increasing demands for more bandwidth and higher data rates in today's networks, wavelength division multiplexing (WDM) is being used extensively in long haul optical transmission systems and is being contemplated for use in short haul applications, such as metropolitan area networks and the like. As is well known, WDM combines many optical channels each at a different wavelength for simultaneous transmission as a composite optical signal in a single optical fiber.
As is well known, an optical transmission system can be configured in a ring topology whereby a plurality of network elements are interconnected by optical fibers. An optical ring network will typically include a plurality of add/drop nodes at which one or more individual wavelength channels can be dropped from or added to the WDM signal that is transported around the ring. Optical ring networks present some unique challenges in contrast to point-to-point configurations and the like. For example, lasing can occur as an optical signal is transported around an optically-amplified ring because the Amplified Spontaneous Emission (ASE) noise of optical amplifiers can experience a net gain as it makes a loop around the ring increasing the power level of the ASE to the point of becoming dangerous or damaging to equipment and personnel as well as adversely affecting system performance. In many configurations, lasing can occur in a short amount of time thus rendering manual-based intervention ineffective. Accordingly, care must be taken in optical ring networks to ensure that the ring does not “close” for any particular wavelength channel transported around the ring, i.e., so that a closed loop is not formed for any given channel.
Provisioning of an optical ring network typically involves a manual process for determining which optical channels of particular wavelengths (hereinafter “optical channels”) are to be used for carrying traffic around the ring between the various nodes. Among other problems, these manual-based provisioning arrangements are generally slow, require involvement of technicians at the various nodes in the network, and are prone to errors that may lead to service-affecting outages on the ring, especially in rings that use extensive add/drop capability.
To facilitate the provisioning process, one common approach is to maintain a database at the various nodes within a network for managing wavelength assignments for optical channels being added, dropped, and routed around the ring network. Entries in the databases indicate associations, whereby an association represents how an optical channel is routed at a particular node. For example, connections are required between ports of different components within a node depending on the provisioning of the optical channel at that node. Associations can be used to specify information such as source port, destination port, wavelength, and so on. By way of example, a source port may be a demultiplexer port that supplies a demultiplexed channel, an output port of an optical translator unit, and so on.
In one commonly employed scheme, an “ADD” association indicates that the optical channel is being added at that node and therefore certain connections between components in the node would be required to implement the “ADD” association. Similarly, a “DROP” association indicates that the optical channel is being dropped at that node and therefore other connections between components in the node would be required to implement the “DROP” association. A “THRU” association is yet another association used to indicate that an optical channel is to be passed through a node, e.g., so-called normal-through or express routing. The aforementioned problem of lasing is a particular concern when “THRU” connections are made at a node because one node may implement a “THRU” connection without knowing whether there is a “break” somewhere else in the ring for that particular optical channel. If a break does not exist, then lasing can occur.